Blanking arrangement for subscription television receivers



Aug. 18, 1953 A. ELLETT 2,649,493

BLANKING ARRANGEMENT FOR SUBSCRIPTION TELEVISION RECEIVERS Filed March5, 1949 4 Sheets-Sheet 2 O- -0- EE 8 1- '2 ['0 66 CO.) .9 as 3.3 2m. 95Q2 (ILL 07 I. r nu:

0 *N ALEXANDERELLETT INVENTOR. 3 W 5 BY HIS AGENT Rec'r. Key

Slgnol A. ELLETT Aug. 18, 1953 BLANKING ARRANGEMENT FOR SUBSCRIPTIONTELEVISION RECEIVERS Filed Ma, rch 3, 1949 4 Shgets-Sheet 4 ALEXANDERELLETT INVENTOR I 3% HIS AGENT Patented Aug. 18, 1953 iTEiD :sr

:Illin'ois Application March '3, 1949,:seria1'No."'z9;425

'3Claims. 1

"Thisinve'ntion relates to television receivers capable of decodingsubscription type coded television signals received over a firstsignalchannel in which' the decoding is effected in response to appropriatedecoding Or key signals received overasecond signal channel.

copendi'ng application serial No. 773,848, entitled Image TransmissionSystem 'by Erwin M. Rosclike, filed September 1'3, -1947, now U. S.Patent No. 254-75598, iss'ued April *3, I951, and assigned to thepresentassigme discloses a subseriptio'n television signalling system ofthe type to which the present invention may be applied. In 'the Roschkesystem a coded television signal is radiated to "subscriber'receiversand 'a 'key signal suitable for decoding the television signal istransmitted to these re'ceivers'over a line circuit, such as a telephoneline. The coding of the television signal is-ac'complished by altering.at spaced time intervals th'e'time relation "between the line trace andline retraceperiodsin' which-the videofrequency components :and thesynchronizingsignal components, respectively, of this signal aretransmitted. The :key signal, transmitted to the subscriber receivers"over existing telephone lines, indicates the times {of occurrence ofsuch alterations in the televisionsignal, so that appropriate correctingapparatus maybe actuated at the receiver to decode the televisionsignal, and thus enable "the receiver to reproduce the image representedby the television signal. In this system, when a receiver is tuned tointercept the coded television signal but, for some reason, thekeysignal is not received, the image reproduced on the screen oftheimagetube moves rapidly back and forth, and a jitter'ed efiect isproduced.

The present-invention is directed .to a system for blanking the imagetube in a receiver during any operating interval in "which asubscription type-televisionsignal-is received but in which the decodingsignal-isnotreceived. This "blanking action ceases when the appropriatekey signal fordecoding the television signal is requested and received..In this manner, a jittered image never appears on-the screen of theimage tube.

It is therefore, an object-of this inventionto provide a system forblanking the image reproducing tube 'of a television receiver, Wheneverthat receiver receives a subscription :type coded television signalbutnot the appropriate key signal required for proper utilization of thecoded signal.

Copending application Serial 'No. 52,909, entitled Coded Sou d :Signallg System, filed October 5, 1948, by George 0. Strikrjnow U. 8. Patent'No. 12,551,068, issued May 1, 1-951, and assigned to the present'ass'ign'e, discloses -"a system in which theasound-frequency componentsof a subscription televisionsignal airebodd. "The decoding of thesesound-frequency components at a subscriber receiver is accom'plishe'dupon the receipt of asuitable decoding or key signal. The presentinvention may-be applied "to such -a system and utilized fo'r'mutin'gthe sound theme of the receiver during any-bperatinginterva1 in which asubscription type of television signal is received but in whichthedeeoding signal is not received. Therefore, through the use of thisinvention the sound channel never passes the sound-frequency componentsin theircoded form to the sound reproducing device, and 'this devicenever reproduces the discordant sounds represented'by'thesecoded-components. v

It is, therefore, *afurthe'r object of this invention :to provide -'asystem for use in a television receiver, by means of which the soundchannel thereof is muted whenever the receiver is tuned to receive'asubscription type television signal, this muting being removed only whenthe appropriate key -signal for decoding :the television signal isreceived.

The features of .thisinvention which 'are'believed' to be new are set-forth with-particularity in "the "appended claims. The inventionitself, however, to'gethe'rwith :further objects and advantages :thereofmay best be understood by ref erence to :the following description whentaken in conjunction with'the accompanying drawings, in which:

Figure 1 shows a subscriber television receiver incorporating oneembodiment of the presentin- Vention,

Figure :2 shows a circuit-diagram o'f this embodiment,

Figure-3 showsasecond type of subscriber receiver incorporating :anotherembodiment of the invention, and,

Figure 4 shows a {circuit diagram of the embodiment utilized .inthe-receiverlof Figure 3.

The subscriber television receiver shown in Figure -1 is similar to thatdisclosed in the aforementioned -Rosch-ke application, but includes ablanking circuit which, iin accordance with the present invention,*blanks the image-reproducing tube duringany 'operatirrg "interval inwhich the receiver intercepts-a subscription'type 'coded'televisionsignal but does not fconcurrently .receive the required key signal fordecoding the television signal. The receiver ofri igure linch'rdes aradio-frequency amplifier and first detector [0, the input terminals ofwhich may be connected to a suitable antenna II. The output terminals ofthe stage iii are connected to the video channel and to the soundchannel of the receiver. The video channel includes the usualintermediatefrequency amplifier and detector I2. The output terminals ofthe detector portion of the stage l2 are connected to a video amplifier[3, which, in turn, is connected through a background reinsertion deviceM, to the control electrode [5, and to the cathode l6 of animage-reproducing tube IT. The sound channel of the receiver comprisesthe usual intermediate-frequency amplifier 18 which is connected to adetector and audio amplifier iii, the output terminals of the stage l9being connected to a suitable sound reproducing device at. The outputterminals of the video amplifier I3 are connected to a synchronizingsignal separator H which, in turn, is connected directly to a verticalsweep generator 22, and through a delay line and switch 23 to ahorizontal sweep generator 24. The vertical sweep generator 22 andhorizontal sweep generator 24 are connected respectively to the verticaldeflection coils 25 and horizontal deflection coils 26 of the image tubeIT. The delay line and switch 23 is controlled by a key signal filterand rectifier and switch operator 21, this operator being connected to aline circuit 28 which extends to the subscription transmitter. Theswitch operator 2'! is also connected to the vertical sweep generator 22by way of leads 29, and to a blanking circuit 30 by way of leads 3|.Input terminals of the blanking circuit 30 are connected to a filter andrectifier 32 by way of leads 33; and the output terminals of thiscircuit are connected to the cathode 16 of the image tube [1 by way ofleads 34, and also to the detector and audio-amplifier unit I9. Thefilter and rectifier 32 is also connected to the sound detector andaudio-amplifier unit 19, as shown.

When the receiver is tuned to accept a subscription type codedtelevision signal intercepted by the antenna II, this signal isamplified and heterodyned to the selected intermediate-frequency of thereceiver, in the radio-frequency amplifier and first detector Ill. Thevideo intermediate-frequency signal is amplified and detected in theintermediate-frequency amplifier and detector i2, and the resultingvideo signals are amplified in the video amplifier l3, and suitablyadjusted as to background level by the reinsertion device M. The signalsfrom the device M are impressed between the control electrode l andcathode E6 of the image tube [1 to control the intensity of the cathoderay in this tube, in the usual manner. The synchronizingsignalcomponents are removed from the received television signal by means ofthe synchronizingsignal separator 2|, and 'the vertical synchronizingsignals are impressed directly on the vertical sweep generator 22 tocontrol this generator and, hence, the vertical deflection of the imagetube IT. The horizontal synchronizing signals are supplied to thehorizontal sweep generator 24 through the delay line and switch 23 tocontrol this generator and, hence, the horizontal deflection-of theimage tube l1.

It will be assumed that the received television signal is coded and thatthe coding is accomplis'hed at the transmitter by altering at spacedtime intervals the time relation between the video-frequency componentsand the horizontal Synchronizing signal components thereof. Th?

delay line and switch 23 is operated between two positions; a first, inwhich the horizontal synchronizing signals are passed to the horizontalsweep generator 24 with no delay, and a second in which the horizontalsynchronizing signals are passed to the generator 24 with a time delaycorresponding to the alteration in time relation between thevideo-frequency components and the horizontal synchronizing-signalcomponents of the received signal. Therefore, when the delay line andswitch 23 is operated at the spaced time intervals of the alteration inthe received signal, the timing of the horizontal deflection. of thetube I1 is altered a corresponding amount, and in an opposite sense tocompensate for such alteration, and the image represented by thereceived television signal is reproduced on the screen of the image tube[1.

The delay line and switch 23 is controlled by the switch operator 21.This operator receives the key signal over the line circuit 28,-thissignal preferably being in the form of bursts of oscillations whichoccur during the spaced time intervals in which the timing between thevideofrequency components and the horizontal synchronizing-signalcomponents of the received television signal has been altered. Inaddition to these bursts of key signal, the operator 2'! receivesvertical blanking pulses from generator 22 and, under the conjointcontrol of the applied signals, operates delay line and switch 23 duringvertical retrace intervals to efiect decoding of the received televisionsignal. In this manner, since changes in timing between thevideo-frequency components and the horizontal synchronizing-signalcomponents from one mode to the other occur during vertical retraceintervals, there is no distortion of the reproduced image, as would bethe case if such changes occurred during trace intervals. The receiverthus far described is fully disclosed in the aforementioned Roschkeapplication, and a further description is deemed to be unnecessary. Itis notedthat when the receiver is tuned to receive a conventionalnon-subscription television signal and no key signal is received overthe line 28, the delay line and switch 23 is in the position in whichthe horizontal synchronizing signals are passed therethrough with nodelay, and the picture tube H reproduces the image represented by suchtelevision signal.

The sound-frequency components of the subscription television signal areamplified in the intermediate-frequency amplifier l8, and detected andagain amplified in the detector and audio amplifier l9, the amplifiedaudio signals being reproduced in the reproducing device 23. It will befurther assumed that the sound carrier wave of the subscriptiontelevision signal is modulated with a blanking signal having apreselected frequency outside of the audio band. This blanking signal isselected from the sound carrier wave and is rectified by means of thefilter and rectifier 32. The rectified blanking signal is supplied tothe blanking circuit 30, which thereupon applies a blocking potential tothe input circuit of the re ceiver image tube I! so that this tube doesnot reproduce the received television signal. Therefore, when thereceiver is tuned to a subscription type of television signal, arectified signal appears at the output of unit 32. Moreover, if theappropriate key signal is not concurrently received over the line 28,the blanking circuit 30 is actuated to blank the image tube IT. Thisblanking of the image tube continues until the required key signal i r qe ted an received over the line circuit 23,

at iwhi-ch'1time1the blanking is removed :from-the image tube :l-"l, in:a ;manner to :be described.

Thereafter, this tube reproduces the corrected image represented by :the:received subscription television signal.

In: subscription systems: of the .typedisclosed intheaaforementionedapplication :Serial No.i52:,909, coding .of thesound-frequency components is effected by .;heterodyning thesecomponents into a range of frequencies outside the :normal sound signalrange. IllSllBh sys uems, thesezcoded :sound components maybeused=to1control *the blanking circuit .30, and no additional blankingsignal is necessary in *theztelevision signal, :itbeingmerely necessaryto .:-arrange thefi'lter "and rectifier so that 'it accepts "signalssolely "in the frequency range of .thBJCOfli-Zd'. sound-frequencycomponents. .It-isa'pparent, that conventional uncoded televisionsignalsreceived bythe present systemihave noeiiect on the blanking icircuitisilas the'uncoded sound-frequency components associated therewithrrenotacoeptedby'thetfilter and rectifier 32.

The blanking :circuit $3.13 .is "shown connected also to the detectorand audio amplifier unit 9 to apply the developed blocking potential tothe cathodeoi" one oithe electron discharge devices includedinthe soundchannel. In this manner, the sound reproducing device 2% is alsoeliec'tively muted during the intervals when the imagereproducing tube Iis blanked.

"Ihe blanking signal has been described as modulated on the soundcarrier wave of the received subscription television signal and selectedfrom the sound channel of the receiver. However, it is to be understoodthat this blanking signal may be transmitted with the subscriptiontelevision signal modulated on the video carrier wave, or in othersuitable manner.

The blanking circuit 38] is shown in detail in Figure '2. Referring'tothis figure, the terminals iii are connected by way of leads '3! to thekey signal filter and switch operator El of Figure l. Une of theterminals ii! is grounded and theother is coupled tothe controlelectrodeil of an electron discharge device 52 through a coupling capacitor 33,the control electrode a: being connected to ground through a grid-leakresistor 4 4. The cathode 45 of the device l2 is connected to groundthrough a resistor 46, shunted by a capacitor 4?. The anode d8 of thedevice 32 is connected to the-positive terminal of a source ofunidirectional potential ie, the negative terminal of this source beinggrounded. The cathode 45 is further connected to the cathode'fie of anelectron discharge deviceii. The terminals 52 are'connected by way ofleads 33 to the filter and rectifier 32 of Figure 1. Qne of theterminals 52 is grounded, andtheother is connected to the controlelectrode 5.3 of the device 5!. The control electrode 53 is connected tothe'negative terminal of a biasing source through a resistor "55, thepos ive terminal of this source being grounded.

' ode 53 of the device 52 isconnected to the c terminal of the source 59through a'resistor 5?, and this anode is further connected to thecontrol electrode 58 of an electrondischarge device 5.9. The controlelectrode 58 is connected to ground-through a'grid-leak'resistor (it.The cathode 82 of the device 58 is connected to ground, and the anode-33 of thisdevice is connected to the positive terminal of thesource-#19 through a resistor 63. The anode $3 is further connected toone of the output terminals 55, the other of these terminals beinggrounded. The ungroundedpterminalfiS is connectedto the cathode 6i'i'ficofcthezimage tube izlzoffrfligure 1-by way ofithe ungronnded leadfii i.

When :the zrecei-ver is tuned :to receive a conventional .uncodedtelevision ssigna'kno signal appears. acrossrthe'sterminals 25:2 fromthe filter and rectifier d2 of Figure .1 because the ordinary broadcast:does snot i'in'clude :the blanking signal to whichunit 232 responds.Alsopno rectified key signal appears across fitherterminals ii! for thereason that :therefismo'line signal during nonsubscriptiontibro'adcasts. Dev-ice R42 :is normally slightly conductive,.andrcathode 4'5 of this device together withicathodea50 of device 5 Itherefore, have a certain positive potential value. .Due to the:negative abias from :the source 54 on the control: electrode53,'.theid'evice is non-conductive. Device 5.9, on the .other hand,:ishighly conductive due to the ,positiveiaiasqon the :control electrode5.8 impressed thereon dcecause of the relatively high :potentialwalue50f anode 5B of the device 5|. The anode1'63 ofithe d-evice 59is'only'slightly positive relativeito ground potential, and there is a:correspondingly :small potential difference between the vleads 2311.The-operating potentials of the image tube kl are reelected in Wellknown manner so .thatthetappli'cation of the small positive potentialtothe-cathode I 6 is not sufficient to blank thisTtube,=that-is,itobiasthe tube to cutoil. 'Consequentlyytheiimage representedby the received:uncoded television signal .is reproduced on the screenithereof.

When-the receiver :is tuned to receive a subscription 'type'co'd'edtelevision"signal, but the subscriberaha-s .notzasyet requestedthat he be supplied with the'key signal required'todeeode this signal;zno rectifiedtkeyrsignalapp'ears across the terminals 40, butazrectified blanking signal of positive polarity from the filter andrectifier 32 of Figure 1 appears acrosscthe'term'inals 52. The amplitudeof the 'rectifiediblanking signal appearing across'terminals 52,:andapplied to the control electrode 53 of'fthe device 5|, is suflicient'toovercome the bias :of the-source Etto render device 5! highlyconductive. 'Theincreased potentialdrop acrosszthe:anodeiresistor 51reduces the conductivity :of device :58, and the anode 63 assumes.an'increased :potenti-al value. "Hence, a substantial positiveapntential existsbetvveen the leads 34, and this potential is sufiicientto bias the cathode ilTB off the image tube H so that this tube tisefficiently blanked Therefore, under these iconditionsinotimage appearson the screen of'theimageitube H.

However, when the subscriber requests and receives the :required keysignal in conjunction with the coded television signal, rectifiedpositive polaritybursts of'th-is-si-gn'al are impressed across theterminals ill]. The time constant of the cathode circuit of device -42,consisting of the resistor 36 and capacitor 37, is long compared withthe max-imum separation of succeeding bursts of the =key-signal so thatthese rectified burstscause the cathode -45 of tube t2 and the cathodeSH-of device "51 to'have a relatively high and substantially constantpositive potential throughout the subscription program. This .increased,potential on .thecathode 5G is sufiicient to render .the device 5|non-conductive. Therefore, the device -.59 becomes highly conductive,and the resulting decrease in potential of the anode -63 decreases theipotential between the leads 134. This .decreasedip'otential between theleads e34 insufficient :to blank the image tube I]. Thus, when the' keysignalisreceived along with the coded television signal, the image tubell correctly reproduces the image represented by the receivedsubscription television signal.

As previously mentioned, the control potential derived from the blankingcircuit 30, during operating intervals when the required key signal isnot received, may be applied to the cathode of a discharge device in thesound channel unit 39 to mute the sound reproducing device 2E5 duringthese intervals. Therefore, by means of the blanking circuit 38 theimage tube H and the sound reproducing device may be blocked eitherseparately or together during these intervals.

Figure 3 shows a second type of blanking, or muting, circuit. Theblanking circuit shown in this figure is connected to a switchmechanically coupled to the receiver tuning device, and functionswhenever the receiver is tuned to a particular signal channel. Theutility of this embodiment is limited to situations wherein thetelevision signal received on the particular channel is of the codedsubscription type at all times, and wherein the channel is not usedalternately for the transmission of coded subscription signals anduncoded television signals. Furthermore, the embodiment of the inventionof Figure 3 is shown as applied to a receiver similar to that disclosedin the aforementioned Striker application in which the sound-frequencycomponents of the received television signal are coded, and acts to muteeffectively the sound reproducing device of the receiver duringintervals when the receiver is tuned to the particular channel, and forany reason the key signal required to decode the sound-frequencycomponents is not received. It is to be understood, however, that themuting system of Figure 3 could quite conveniently be used to blank thereceiver image reproducing during such intervals, if so desired.

The receiver of Figure 3 is in many respects similar to that of Figure1, and includes a radiofrequency amplifier and first detector In coupledto an antenna H, a video intermediate-frequency amplifier and detectorI2, a video amplifier l3 and a background reinsertion device 54, thesestages being connected in cascade as previously. The output terminals ofthe device M are connected between the control electrode I5 and cathode[6 of an image tube IT. The video amplifier I3 is connected to asynchronizing-signal separator 2|, which in turn is connected to avertical sweep generator 22 and to a horizontal sweep generator 24. Thevertical sweep generator 22 is connected to the vertical deflectioncoils 25 of the image tube I1, and the horizontal sweep generator 24 isconnected to the horizontal deflection coils 26 of this tube.

The receiver thus far described in quite conventional, and televisionsignals received on the antenna II are amplified and heterodyned to theselected intermediate frequency of the receiver in the stage H0. Thevideo intermediate-frequency signals from the stage H] are amplified anddetected in the intermediate-frequency amplifier and detector [2, andthe resulting video signals are amplified by the amplifier l3. Thesesignals, suitably adjusted as to background level by the device 14, areused to control the intensity of the cathode ray in the image tube H.The synchronizing signals are removed from the video signal by means ofthe separator 2 I, and the vertical synchronizing signal is impressed onthe vertical sweep generator 22, while the horizontal synchronizingsignal is supplied to the horizontal 8 sweep generator 24, therebycontrolling these generators and the deflection of the cathode ray inthe image tube H.

The stage In is also connected to a sound intermediate-frequencyamplifier and detector I0, and the output terminals of this detector areconnected to a decoding circuit H. The decoding circuit H is coupled toan audio amplifier 72 which in turn is connected to a sound reproducingdevice 13. A sine wave having the frequency of the horizontalsynchronizing signal is obtained from the horizontal sweep generator 24and impressed on a gate circuit 15 by way of leads 16. The outputterminals of the gate circuit 15 are connected to the decoding circuit Hby way of leads H. As previously, bursts of key signal are received fromthe subscription transmitter over the line circuit 23, and these burstsare rectified in a key signal filter and rectifier 13. The outputterminals of the rectifier is are connected to the gate circuit :5 bymeans of leads l9, and these terminals are also connected to the inputterminals of a blanking circuit by way of leads 8|. The blanking circuit85 has further terminals connected to a rotary switch 82 by means ofleads 83. The switch 82 is mechanically coupled to the receiver tuningdevice, and one of the leads 83 is connected to the movable arm 5d ofthis switch, while the other is connected to a contact 85 thereof.Whenever the receiver is tuned from one signal channel to another, themovable arm 84 connects with the various contacts of this switch, andwhen the receiver is tuned to receive a subscription type codedtelevision signal the arm 84 connects with the contact 85, thus closingthe connection across the leads 83.

The particular receiver represented in Figure 3 is adapted to decode asubscription television signal of the type in which only thesound-frequency components thereof are coded. A system of that type isdescribed in the aforementioned Striker application, wherein coding ofthe sound-frequency component is effected by heterr odyning thiscomponent at the transmitter with a signal having the frequency of thehorizontal synchronizing-signal component of the television signal.Therefore, at the receiver it is necessary to produce an identicalsignal to decode the sound-frequency component. This decoding signal maybe obtained from the horizontal sweep generator 24 and is impressed onthe decoding circuit H through a gate circuit '55. When the key signalis received over the line circuit 28 and rectified in the rectifier 18,the gate circuit "i5 is energized to pass the decoding signal and thereproducing device 13 reproduces the sound-frequency components of thereceived television signal as more particularly explained in the Strikerapplication.

Should the receiver be tuned to receive the coded television signalduring a period when no key signal is received on the line circuit 23,the gate circuit 15 does not pass the decoding signal and thesound-frequency component is delivered to the reproducing device 13 inits coded form, resulting in unintelligible sound. To avoid this, theblanking circuit 80, in the absence of the rectified key signal on leads8! mutes one of the stages of the amplifier 12, and no signal isreproduced by the device i3 until the rectified key signal is impressedon the circuit 89 by means of the leads 8!. It is noted that when thereceiver is tuned to receive a conventional nonsubscription signal, andno key signal is received on the line 2's; the'gat'e "ir the decodingsignal from Therefore,nodecodingsign' V decoding circuit TI, and this ne1 actssv a conventional amplifier and passes the" encoded soundcomponents from stage to" the audio amplifier l2.

The blanking ci'rcuit80 of Figure 311s own in detail in Figure 4'. Itincludes terminals" 8' 5 connected to thekey"sigIiaTrectifieTIB ofF Q 3by means of the leads'd'l'. Oneof meter als 86 is grounded and the otheriscdiipled to the control electrode 8'! of an i e le ctrortischa ge" asvice 88 through a' coupling capacitor 89; this control electrode beingconnected to ground through a grid-leak resistor 90 The cathode 9| ofthe device 88'is' connected t ground through a resistor 9-2 shunted by"a capacitor 93. The anode 94* of the device 88 is'directly connectedto'the positive terminal of a source of unidirectional potential 95, thenegativeterminal'o'f this source being grounded. The cathode 9|. of thedevice 38 is connected to .the cathode'fili of an electron dischargedevice 97.

A secondpair of terminals98is connectedto the contact 85 and the movablearm 84of' the rotary switch 82 of Figure 3"by" means of'th'e leads 83.One of the terminals90 is connected to the control electrode 99 ofthe"device'97, and the other is connected to the positive terminal of aunidirectional potential-source I00, thenegative terminal of thissource-being: grounded; The control electrode 99 is also connected tothe negative terminal ofa'biasing source IOI through a resistor I52, thepcsitiv'fterlr'ninal of this source being grounded. The afio'de 'l03 ofthe d evice 9! is connected to the positive terminal of the source 95through a resistor I04, and this anode is further connected to thecontrol electrode I05 of the device I 06. The control electrode I05 isconnected to ground through a grid-leak resistor till, and the cathodeI08 of this device is connected directly to ground. The anode I09 of thedevice Q06 is connected to the positive terminal of the source 95through a resistor III), and this anode is further connected to one ofthe output terminals III, the other of which is connected to ground. Theterminals II I are connected between ground and the cathode of thedischarge device in the audio amplifier I2 of Figure 3.

When the receiver is tuned to a conventional, non-subscriptiontelevision transmitting station, no rectified key signal appears acrossthe terminals 85, and the position of the rotary switch 82 is such thatthe terminals 98 are open circuited. Under these conditions, the device91 is non-conductive due to the negative bias on the control electrode99 from the biasing source illI. Accordingly, the control electrode I 04of the tube IE5 is at a relatively high positive potential and thedevice I06 is highly conductive. The potential of the anode I09 is onlyslightly above ground potential and the potential across terminals 5 I Iis insufficient to mute the device of the audio amplifier I2 of Figure3. Thus, the reproducing device I3 is permitted to reproduce the audiosignals accompanying the received television signal.

When the receiver is tuned to the subscription television signalchannel, the arm 84 of the switch 82 of Figure 3 engages the contact 85.If, when the receiver is tuned to this channel, the key signal requiredto decode the subscription signal is not received, no signal appearsacros the terlis iin'pr s'sedon' the l0 B'y' reason of the switch 82closing between thejterminals fiil, a positive b'iasirrdih he source I00isimpressed upon the control electrode 99, and this positive biasoverc'ciiiiesthengativ biasfrom the source I M, and niece/ice 91'becomes highly conductive. The potential drop across the resistor I941is now increased; andtha space current flowing through the device IDSismaterially decreased. The potent of anode I09 increases, and thepotential acr ss thef teim n als" I II is correspondingly in- Theniutingpotential thus presented at I I'I- is utilized a a cathode biasing t 'l"a discharge device in the audio r'lZofjfigure 3 to bias that device toand'eifectively mute this amplifier. Under s, the reproducing device I3does e the coded audio signals. when the required key signal is'redjreceive d' jointly with the coded sig- I y T b orrectified key signalhaving a positive" polar ty; appear across the terminals 86. constant ofthe cathode network 92,

The time 931s long relative to the maximum separation of succeedingbursts of the rectified key signal, andthese bur sts cause the potentialof cathode fl'of device t8, and cathode 96 of device 9! to The increasedpositive bias on the cathod 9li is sufficient to render the device 97at}; conductiveand the device I06 highly conductive; The potentialacrossthe terminals II I is" again reduced to such a value that theamplifier ir cglrigure 3 is no longer muted, and the reproducingdevice13 reproduces the dc ed di sign lsv The circuit. ,Qf Fi ure} showstheswitch 82 of Figure 3 with leads 83 connected between the arm 8d anda single contact 05. It i evident, however, that when there is more thanone subscription signal channel, the leads 83 may be connected to eachcontact in the switch corresponding to a subscription signal channel.

This invention provides, therefore, blanking or muting circuits for usein a television receiver, whereby the receiver is initially blanked ormuted, or both, whenever it is tuned to receive a subscriptiontelevision signal, and this blocking of the receiver is removed onlywhen the key signal required to decode the television signal isrequested and received. Therefore, distorted images are not reproducedon the screen of the receiver image tube, and discordant sounds are notreproduced by the sound reproducing device whenever the receiver istuned to a subscri tion signal and the decoding key signal is not alsoreceived.

The invention has been described in conjunction with televisionreceivers, since the usual subscription type of signalling system is ofthe television type. However, it is apparent that the muting circuitsdescribed herein may be used in such systems where sound signals onlyare transmitted, and as shown particularly in Figure 3, the sound signalreceiver may be muted Whenever it is tuned to a subscription soundsignal channel, until the appropriate key signal for decoding thesubscription signal is received.

While specific embodiments of the invention have been shown anddescribed, modifications may be made, and it is intended in the appendedclaims to cover all such modifications as fall within the true spiritand scope of the invention.

I claim:

1. A wave-signal receiver for utilizing a coded modulated electricalsignal and for concurrently utilizing a key signal to decode the codedsignal, said receiver comprising: an intelligence-reproducing device;circuit means for demodulating said electrical signal and for utilizingthe demodulated signal to actuate said reproducing device; decodingapparatus coupled to said circuit means and responsive to said keysignal for decoding said coded signal; a network coupled to said circuitmeans and responsive to said coded signal for disabling said reproducingdevice during reception of said coded signal by said receiver; and acontrol circuit coupled between said circuit means and said network andresponsive to said key signal for disabling said network.

2. A wave-signal receiver for utilizing a coded modulated electricalsignal including a blankingsignal component and for concurrentlyutilizing a key signal to decode the coded signal, said receivercomprising: an intelligence-reproducing device; circuit means fordemodulating said electrical signal and for utilizing the demodulatedsignal to actuate said reproducing device; decoding apparatus coupled tosaid circuit means and responsive to said key signal for decoding saidcoded signal; a network coupled to said reproducing device andresponsive to an applied signal for disabling said reproducing device; afilter circuit coupled to said circuit means for applying saidblanking-signal component to said network to actuate said network; and acontrol circuit coupled between said circuit means and said network andresponsive to said key signal for disabling said network.

3. In a wave-signal receiver including a tuning device for tuning saidreceiver to utilize a coded modulated electrical signal, said receiverconcurrently utilizing a key signal to decode the coded 12 signal: anintelligence-reproducing device; cire cuit means for demodulating saidelectrical signal and for utilizing the demodulated signal to actuatesaid reproducing-device; decoding apparatus coupled to said circuitmeans and responsive to said key signal for decoding said coded signal;a switching device mechanically coupled to said tuning device; a networkcoupled to said reproducing device and controlled by said switchingdevice for disabling said reproducing device when said receiver is tunedto receive said coded signal; and a control circuit coupled between saidcircuit means and said network and responsive to said key signal fordisabling said network.

ALEXANDER ELLETT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,251,525 Rosenthal Aug. 5, 1941 2,306,435 Graham Dec. 29,1942 2,307,728 Mertz Jan. 5, 1943 2,392,672 Koch Jan. 8, 1946 2,402,067Mathes June 11, 1946 2,405,252 Goldsmith Aug. 6, 1946 2,406,811Deloraine Sept. 3, 1946 2,414,101 Hogan Jan. 14, 1947 2,419,568 LabinApr, 29, 1947 2,472,774 Mayle June 7, 1949 2,480,115 Brown Aug. 30, 19492,546,987 Eannarino Apr. 3, 1951 2,547,598 Roschke Apr. 3, 1951 FOREIGNPATENTS Number Country Date 386,849 Great Britain Jan. 26, 1933

